Voice screen



April 29, r1930- w. F. SMITH, JR., ET AL VOICE SCREEN Filed Oct. 29, 1927 fiaf . 771 RABT/it't' 5r A14 Arm/m5) Patented Apr. 29, 1930 MNITEO STATES 1 WALTER F. SMITH, JR., OF NEW YORK,

ATENT OFFICE AND THEODORE n. cRABTREE, OF NEW BRIGHTON, N W YORK, ASSIGNORS To BELL TELEPHONE LABORATORIES, INCOR- SPORATED, OF NEW YORK, N. Y., A CORPORATION OF EW YORK VOICE SCREEN Application filed October 29, 1927. Serial NO. 229,558.

I This invention relatesto voice screens and 1s an improvement over the type disclosed in Patent Np. 1,688,995-of Oct. 23, 1928, to W. F..

vided whereby sound waves of high fre-.

quencies, which would be intelligible to persons in the Vicinity of the user, are suppressed and those of low or unintelligible frequencies are exhausted in the atmosphere. V

In these devices, du to the fact that the speaker talks directly into the mouthpiece, I and that most of the energy is contained in sounds below 350 cycles per second, the volume eflicien'cy or A. 0. output 'has been found to be too high in that range of frequencies, which materially affects the quality of transmission, by rendering the sounds hollow at the receiver end of the telephone line.

While the provision of a high pass filter between the muflier and the transmitter diaphragm has been found to be satisfactory as far as speech transmissionis concerned, such high pass filters increase the, size of the muffler to an objectionable dimension and greatly increase its cost of manufacture.

It is the object of this invention to reduce the size of the muffler and its. manufacturing cost. In accordance with this invention thefunction heretofore performed by thehigh pass filter is accomplls'hed by providing the dia-- phragm with a number of apertures leading to a chamber formed by the rear electrode and the diaphragm, these apertures at low speech frequencies permitting the pressure variations to be partially transmitted to the air chamber, whereas at high speech frethe apertures offers such a high impedance to the transmission of .the pressure that the pressure equalizing effect referred to is practically zero at these frequencies.

Other features of the invention and advantages will appear from the following-description and by the claims appended thereto, reference being made to the accompanying drawing in which:

mentioned.

' quencies the inertia of the air in and around Fig. 1 is a side view of the device partially in section; and

Fig. 2 is a front view of the transmitter showing a number of parts partially cut away.

This transmitter consists of a bod ring 10, which issecurely attached to an or inary transmitter shell 11 by a number of screws 12.

On the ring 10 is screwed a ring 13 which is provided with an outwardly flared ridge adapted to receive a mouthpiece 14 which may be made of rubber or any other yieldable material arranged to snap in position on the flared. ridge of ring 13 as shown in Fig. 1. In the middle portion of ring 10 there is provided a number of radially disposed holes 17, 18 and 19 shown in Fig. 2, which register with similarly sized holes 17 18' and 19 in a ring 16. Holes 17, 18 and 19' in ring 16 connect directly with an annular chamber 20 by a number of holes 21, 22 and 23. Holes 17 18' and 19', and 21,22 and 23 and cham ber 20 thus formed, cooperate to form a low pass filter system of the type used in the mufller disclosed in the application above In ring 10, adjacent the bell 11, there is mounted a microphone which is supported and insulated from the ring 10 by rings 25,

26 and 27 which may be made ofv any suit,-

able insulating material. 7 Rings 25, 26 and 27 together with electrode 24 are held securely in adjusted position in ring 10 by means of ring 28 fastened on the ring 10 by a number of screws 29.

Electrode 24 is provided with an interiorly' threaded portion 31 in which the electrode 32 is mounted and insulated therefrom b rings 33 and 34 and at its periphery'by circular air space as shown. Electrode 32 and insulating rings 33 and 34 are held in adjusted position by ring 35 screwed in the threaded portion 31 0f electrode 24. In electrode 24-thre is mounted a truncated cone shaped diaphragm 36 which is yieldably held at its periphery by a number of paper rings arranged to form pile-ups 37 and 38 disposed on each side of the diaphragm, and held 1n adjusted positiontherein by. a metal ring 43 on which screens 44 and 4.5 are mounted.

Electrode 24 is rovided with a circular ridge 39 adapted or holding aknumber of paper rings 40' in position coaxially with respect to the effective surface of electrode 24. These paper rings cooperate with the truncated portion of the diaphragm for holding the resistance varying material in the chamber formed by electrodes 24 and 32 and an insulating ring As shown in Fig. 1, electrode 24: including ridge 39 and the paper ring pile-up 37 cooperate with the diaphragm 36 to form a chamber 41 which connects with the interior of the mufiier by a number of apertures 42.

feet of the apertures is thus to diminish the effective driving force at low frequencies without affecting the operation of the device se high frequencies.

The degree of frequency discrimination in the action is dependent on the size of the apertures, which determines the inertia of the wave path through the diaphragm, and also 1 upon the size of the air chamber behind the diaphragm, since a given flow of air through having apertures therein and a sound chamber behind said diaphragm, the size of the apertures and the dimensions of the chamber being such as to permit the pressure varia- 4 tions at low speech frequencies to be partially transmitted to the said chamber and so bring about a partial equalization of the resultant pressure acting on the diaphragm and at high speech frequencies offering a large impedance to the transmission of the pressure to the chamber.

3. A telephone transmitter comprising a pair of electrodes, resistance varying material in contact with said electrodes, a perforated diaphragm for actuating the resistance varying material, the size of the perforations in said diaphragm being such that the effec-- tive driving force of the air waves is diminished at low speech frequencies and not affected at high speech frequencies.

In witness whereof, we hereunto subscribe our names this 27th day of October, A. D.

- WALTER F. SMITH, JR. THEODORE H. CRABTREE.

the apertures will build up a larger pressure p in a small chamber than in a large one.

The dimensions which have been found suitable are .035 for the diameter of the apertures, eight in number, located midway between the edge of the button and the periphery of the diaphra m, and .1 cu. in. for the volume of the charm er. a

The leakage path formed around the edge of the diaphragm by the paper damping rings is of such high impedance compared to that afforded by the holes in the diaphragm that 1t may be ignored since it does not materially affect the operation of the device,

What is claimed is:

1. In a transmitter, a diaphragm having a I number of apertures, and, a sound chamber behind saiddiaphragm, said diaphragm being so perforated and the dimensions of said .chamber being such as to cause the pressure at low speech frequencies to be partially transmitted to the chamber, and to ofier such alarge impedance to the highspeech frequem sq c1es that the equalizing efiect is substantially zero at such frequencies. 1

2. ha telephone transmitter, a mouth- I piece, a microphone, a diaphragm for operatr ing the microphone in response to sound waves impinged on said diaphragm, said diaphragm 

